The present invention relates to novel nitrification inhibitors of formula I. Moreover, the invention relates to the use of compounds of formula I as nitrification inhibitors, i.e. for reducing nitrification, as well as agrochemical mixtures and compositions comprising the nitrification inhibitors. Further encompassed by the present invention are methods for reducing nitrification, said methods comprising the treatment of plants, soil and/or loci where the plant is growing or is intended to grow with said nitrification inhibitors and methods for treating a fertilizer or a composition by applying said nitrification inhibitor.
Nitrogen is an essential element for plant growth and reproduction. About 25% of the plant available nitrogen in soils (ammonium and nitrate) originates from decomposition processes (mineralization) of organic nitrogen compounds such as humus, plant and animal residues and organic fertilizers. Approximately 5% derive from rainfall. On a global basis, the biggest part (70%), however, is supplied to the plant by inorganic nitrogen fertilizers. The mainly used nitrogen fertilizers comprise ammonium compounds or derivatives thereof, i.e. nearly 90% of the nitrogen fertilizers applied worldwide is in the NH4+ form (Subbarao et al., 2012, Advances in Agronomy, 114, 249-302). This is, inter alia, due to the fact that NH4+ assimilation is energetically more efficient than assimilation of other nitrogen sources such as NO3−.
Moreover, being a cation, NH4+ is held electrostatically by the negatively charged clay surfaces and functional groups of soil organic matter. This binding is strong enough to limit NH4+-loss by leaching to groundwater. By contrast, NO3−, being negatively charged, does not bind to the soil and is liable to be leached out of the plants' root zone. In addition, nitrate may be lost by denitrification which is the microbiological conversion of nitrate and nitrite (NO2−) to gaseous forms of nitrogen such as nitrous oxide (N2O) and molecular nitrogen (N2).
However, ammonium (NH4+) compounds are converted by soil microorganisms to nitrates (NO3−) in a relatively short time in a process known as nitrification. The nitrification is carried out primarily by two groups of chemolithotrophic bacteria, ammonia-oxidizing bacteria (AOB) of the genus Nitrosomonas and Nitrobacter, which are ubiquitous component of soil bacteria populations. The enzyme, which is essentially responsible for nitrification is ammonia monooxygenase (AMO), which was also found in ammonia-oxidizing archaea (Subbarao et al., 2012, Advances in Agronomy, 114, 249-302).
The nitrification process typically leads to nitrogen leakage and environmental pollution. As a result of the various losses, approximately 50% of the applied nitrogen fertilizers are lost during the year following fertilizer addition (see Nelson and Huber; Nitrification inhibitors for corn production (2001), National Corn Handbook, Iowa State University).
As countermeasures the use of nitrification inhibitors, mostly together with fertilizers, was suggested. Suitable nitrification inhibitors include biological nitrification inhibitors (BNIs) such as linoleic acid, alpha-linolenic acid, methyl p-coumarate, methyl ferulate, MHPP, Karanjin, brachialacton or the p-benzoquinone sorgoleone (Subbarao et al., 2012, Advances in Agronomy, 114, 249-302). Further suitable nitrification inhibitors are synthetic chemical inhibitors such as Nitrapyrin, dicyandiamide (DCD), 3,4-dimethyl pyrazole phosphate (DMPP), 4-amino-1,2,4-triazole hydrochloride (ATC), 1-amido-2-thiourea (ASU), 2-amino-4-chloro-6-methylpyrimidine (AM), 5-ethoxy-3-trichloromethyl-1,2,4-thiodiazole (terrazole), or 2-sulfanilamidothiazole (ST) (Slangen and Kerkhoff, 1984, Fertilizer research, 5(1), 1-76).
Furthermore, pyrazole-based nitrification inhibitors have been described, e.g., in U.S. Pat. No. 3,635,690, WO 2011/009572, WO 2011/015305, DE 10 2011 120 098, and DE 10 2013 022 031 B3. U.S. Pat. No. 3,635,690 describes 1-propynyl pyrazole, i.e. 1-prop-1-ynyl pyrazole with an internal triple bond, as nitrification inhibitor. Phenylacetylene, wherein the triple bond is a terminal triple bond, is described as nitrification inhibitor in U.S. Pat. No. 4,552,581.
However, many of these inhibitors only work sub-optimal. In addition, the world population is expected to grow significantly in the next 20-30 years, and, therefore, food production in sufficient quantities and quality is necessary. In order to achieve this, the use of nitrogen fertilizers would have to double by 2050. For environmental reasons, this is not possible, since nitrate levels in drinking water, eutrophication of surface water and gas emissions into the air have already reached critical levels in many places, causing water contamination and air pollution. However, fertilizer efficiency increases significantly and less fertilizer may therefore be applied, if nitrification inhibitors are used. Therefore, there is a clear need for novel nitrification inhibitors, as well as for methods using them.
In particular, there is a need for nitrification inhibitors with a high activity.
Furthermore, there is a need for nitrification inhibitors which are effective at low amounts, as low application rates typically result in economical and environmental advantages.
It was therefore the object of the present invention to provide improved nitrification inhibitors in view of the prior art.